An outphasing amplifier with a non-isolating combiner is an amplifier circuit that can provide substantially high power efficiency over a wide input range. However, the efficiency of such amplifier circuit drops quickly in the low power region, which can reduce the overall efficiency for amplifying a modulated waveform with a large peak to average power ratio. Moreover, the driver to the power amplifier (PA) in the circuit is always running at maximum power, and therefore dissipating power even at low amplifier power output, causing further degradation of the overall power efficiency of the system. While a high efficiency digital driver can be established with a pulse width modulation (PWM) technique, such driver lacks the dynamic range to support backed-off linear operation. There is a need of an improved architecture for the outphasing amplifier with a non-isolating combiner that overcomes such issues to improve overall power efficiency of the system.